Multi-segment Winding Application for Axial Short Circuit Force Reduction Under Tap Changer Operation in HTS Transformers

High-temperature superconducting (HTS) transformers have remarkable appealing advantages over conventional ones. But higher brittleness of HTS windings with respect to copper windings makes HTS transformers more vulnerable in short circuit and inrush current situations. During tap changer operation, appreciable asymmetry and non-uniform distribution of ampere-turn along the windings causes high axial component of short circuit forces and makes the situation more severe. In this paper, multi-segment winding method is employed for reduction of axial short circuit forces. An analytical method is presented for calculation of axial component of short circuit forces under tap changer operation. Analytical method shows that with utilizing HLHLHLH asymmetrical multi-segment windings, during tap changer operation, the axial component of short circuit forces reduces significantly. The results of the analytical method are compared with the results of finite element method (FEM) model simulations, and the consistency is demonstrated.